Higher plants reported to be active against gram-negative and tubercular organisms are being reexamined by modern screening procedures. Those showing reproducible in vitro bioactivity are being fractionated and the active principles are being isolated in pure form. These are evaluated microbiologically and pharmacologically by comparison with clinically used antibiotics. They are also identified structurally to allow testing of similar substances. Preparation of analogous materials by chemical synthesis, especially in cases where the isolation yields are low, allows determination of the effect of structure on bioactivity. This is especially important for these materials are chemically unlike any currently available antibiotics. It is anticipated that this work will open new avenues for research in the antibiotic area at a time when new approaches are desperately needed.